under water weapon is a slut.

Ruby and Emerald in FF7 were easy, but VERY time-consuming.

Ultima weapon in FF8 wasn't that bad either, just needed to watch out for his Light Pillar which killed a character in 1 hit.

Omega weapon in FF8 though, that's probably my worst boss, quite frustrating. >_<

FF7 ruby and emerald. It was a disapointment that sephrioth died so easy.
ff8 First time I played it unltimecia was hard as hell, but definetly ultimate and omega weapon were hardest.
Played ffx didn't beat it so can't really give an answer. I was fighting sin when I quit playing.

where did u fight sin, in the end you fight him about 3 times (i havent played for a while, i broke my PS2 so it may be wrong)

im going to have to go with ff7's emerald weapon... i still couldnt even come close to killing him at around 65-70 (i think) with kotor and mime. im sure with some work i couldve taken him down quite easily, but he's considerably harder than the final boss, which (as far as i can remember) isnt too common in ff games

lol i was playing ff x-2 and Trema at the end of Via Infinito was super annoying Cat Nip in that game is the best ever!

I gotta say I had the most trouble in ff10 with that seymore dude on the mountain.

There are several bosses which has given me challenge due bad chars or wrong chars.
FF7 : All bosses. Weapons and even Sephiroth (last one) in the end of the game. Maybe since all my characters were still 40-55 lvls.. I tried pathetically to lvl them in last place but I died to normal enemies there x]
FF8 : I completed whole game like 5 times, and I never had so much trouble with any boss. If it went tough, I casted aura on Squall and let Lionheart sing.
FF9 : Last boss. Lol, I didnīt bother to exp my characters in this game either, so went to last boss with like 50~ lvl characters.
FF10 & FFX-2 : Maybe this thing, underwater monster in Monster Arena, since I dislike Wakka and Rikku so didnīt bother to lvl them. Nemesis was hard too. Also Dark Aeons a.a

I think so far the hardest bosses were in FF10 for me. Hard to decide which one ^^

Penance is easily the hardest boss in ff10, followed by trema in ff10-2. You can't deny that unless you haven't actually tried them As it required you to kill all the dark aeons/ get down to floor 100 in bevelle to get to them, which is also very hard... penance had stupidly high stats and HP and trema was fast and dealt out alot of damage...

Out of the ones I've played its between emerald weapon from FFVII and omega weapon from FFVIII. I guess it depends wether you choose to use the holy wars in FFVIII, which makes things much much easier